Waaaaaaaah…! The Chinese raws are out for Chapter 21 and Estella has already translated them! You can find the summary at bxsmanaga: here. I can’t really say much without spoiling it, so please go and check it out… the only spoilers I’ll give here are:

Narumi turns out to be bit of a mean girl (kind of surprised that Sakisaka-sensei made her that way, but I guess it makes it easier to dislike her)